The value type of the attribute can be specified by either overriding the typeBuilder field on the AttrDef, or by providing a parameter of type `AttributeSelfTypeParameter`. This removes the need to define custom storage class constructors for attributes that have a value type other than NoneType.
Differential Revision: https://reviews.llvm.org/D97590
The support for attributes closely maps that of Types (basically 1-1) given that Attributes are defined in exactly the same way as Types. All of the current ODS TypeDef classes get an Attr equivalent. The generation of the attribute classes themselves share the same generator as types.
Differential Revision: https://reviews.llvm.org/D97589